Process of coloring anodized aluminum



United States Patent 3,019,143 PROCESS OF COLORING ANODIZED ALUMINUM Rolf Dessauer, Brandywine Hundred, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Oct. 21, 1959, Ser. No. 847,703

5 Claims. (Cl. 1486.1)

This invention relates to a process for coloring anodized aluminum and more particularly to an improved solvent process for coloring anodized aluminum wherein metallized azo dyes are applied to the surface of the anodized aluminum from an organic solvent solution.

It is well established that dyeings possessing some acceptable light-fastness are achieved on anodized aluminum when the aluminum is properly anodized and the surface sealed after dyeing by treating it-with boiling water or steam. Heretofore anodized aluminum has usually been dyed with acid dyes in aqueous solution. The current practice of dyeing anodized aluminum with water soluble dyes is described in Dyestuffs, vol. 41, No. 8, December 1956. When utilizing the aqueous dyeing technique it has been found that the depth of shade obtained is often limited, especially on thin polished anodized surfaces, and also the colored aluminum does not exhibit sufficient lightfastness to make it useful for exterior applications under weathering conditions. Further shortcomings of the aqueous dyeing procedures include the use of extended periods of dyeing in Order to obtain a deep penetration of dye into the oxide coating on the aluminum and, when dyeing froman generally necessary to follow the initial dyeing by higher temperatures and these higher temperatures seal the coating and stop the dye absorption.

Non-aqueous solvents have been disclosed as being use aqueous bath at room -tempera-ture, it is ful for dyeing anodized alimiinumfThese solvent system's" include alcohols, benzene, acetone, pyridine, oil varnish, fat and mineral spirits. When using" these organic solvent systems it has not been possible to obtain concentrated solutions of the high molecular Weight light-fast dyes and the organic solvent procedure does not avoid the many problems such as poor light-fastness, slow dyeing and lack of depth of shade, which are presented when an aqueous dye procedure is employed. It is quite apparent that it would be highly desirable to provide an improved process for dyeing anodized aluminum whereby the problems and disadvantages of the prior art procedures are overcome.

It is an object of the present invention to provide an improved solvent process for coloring anodized aluminum. A further object is to provide a process for rapidly coloring anodized aluminum in level shades at ambient temperatures. A still further object is to provide a process for coloring anodized aluminum in either light or heavy shades having excellent fastness to light. Other objects will appear hereinafter.

These and other objects of this invention are accomplished by the improvement in the process for coloring anodized aluminum with a dye followed by sealing of the dye in the aluminum oxide coating by means of steam or hot water, which comprises employing as a solvent for the dye a compound selected from the group consisting of dimethylformamide, diethylformamide, dimethylacetamliquid portion of ide, diethylacetamide and dimethylsulfoxidc. The process of the present invention is similar to the prior art procedures in that the anodized aluminum is colored by means of a dye and the dye is then sealed in the aluminum oxide coating by use of steam or hot water. The essence of this invention consists in the use of a particular organic solvent for the dye. By means of the present invention it is now possible to dye anodized aluminum with a wide variety of dyes including both the water-soluble and water-insoluble species in a rapid manner and in a wide variety of strengths. This process is devoid of the numerous problems associated with the prior art procedures, particularly light-fastness, in that the colored anodized aluminum displays a light fastness of at least 500 Fade- Ometer hours.

In carrying out the process of this invention any of the dyes which have been employed heretofore for coloring anodized aluminum may be used. The process is particularly applicable with the chromium or cobalt complexes of the o,o-dihydroxy or o-hydroxy-o-carboxy azo dyes. If desired, these dyes may contain water solubilizing groups; however, it is to be understood that the improved results from the process of the present invention are obtained when either water-insoluble or water-soluble dyes are employed. As noted above, any of the dyes normally used in coloring anodized aluminum may be employed. These include the chromium or cobalt complexes of monoor poly-azo dyestuffs as Well as the complexes of anthraquinone derivatives, triarylmethane dyestuffs, azines, thiazines or oxazines. Specific dyes which may be employed-include those used in the examples; those which are listed in Colour Index, second edition, under C. I. Nos. 14006, 13900A (Solvent Yellow 19), 1 8745 (Solvent Orange 5), 19351, 18736, 15685, 19115, 16055, 16260, 13425, 15711, 62105, 62085, 63010, 17045 and 34220; 3'-liydroxy quinophthalone, 1-hydroxy-4-anilino anthraquinone and 2,2,4,4'-tetrahydroxybenzophenone.

In accordance with the present invention the dyes are applied to the anodized aluminum by employing, as a solvent for the dye, an organic compound which is either dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide or dimethylsulfoxide. Mixtures of these compounds may be used. These solvents may constitute the entire liquid vehicle or, for reasons of economy,

may be reduced to as little as 5 percent other solvents. Thus the solution of tain anywhere from 5 to percent of the vehicle with the dye may conby Weight of the a solvent which is either dimethylformamide, diethylformamide, dimethylacetamlide, diethylacetamide or dimethylsulfoxide. Suitable other solvents which may be employed to dilute the liquid vehicle for the dye include alcohols, such as methanol, ethanol and butanol; ketones, such as acetone and methyl ethyl ketone; hydrocarbons, such as benzene, toluene and heptane; ethers, such as dioxane; glycols, such as ethylene glycol; polyglycols and their ethers, such as 2-ethoxyethanol and carbitol; basic compounds, such as pyridine and quinoline; and chlorohydrocarbons, such as carbon tetrachloride and chlorobenzene.

When employing the special solvents of the present invention the dye enters the anodized surface of the aluminum in higher concentration and as a result it is possible to produce deeper dyeings than by the prior art proce- 3 dures even on thin polished anodized surfaces. In addition, these solvents yield more level dyeings and, also, when the dye is properly selected and properly sealed in the anodized surface, the stability of the colored aluminum to light is quite outstanding.

The process of the present invention permits great flexibility in the application of the dye to the anodized aluminum. Painting, printing, spraying or dipping procedures may be employed. In general it is preferred to carry out the dyeing procedure at ambient temperatures; however, the anodized aluminum may be coated at lower or higher temperatures. Temperatures of from room temperature up to the boiling point of the solvent may be used.

.The concentration of the dye in the solution which is used to coat the anodized, aluminum is not critical. High concentrations of the dyes make possible the production of deepshades, particularly when water-insoluble dyes are employed. However, it is to be understood that concentrations below saturated solutions may be used. The concentration depends on the dye and depth of shade desired. Solutions up to and including saturated solutions may be used.

'When coating the anodized aluminum in accordance with the present invention the time factor involved is not critical. Thus, the anodized aluminum may be immersed in the dye solution for a period of time ranging from about 5 seconds to30 minutes depending on the depth of shade desired. The longer time periods may be used to advantage in the exceptional cases where the dyes have low solubility or in the case of dyeing very thin oxide coatings.

The process of the present invention overcomes the numerous problems associated with the prior art procedures. By using the solvents of this invention a wider variety of dyes can be used to color anodized aluminum since one isno longer limited to the water soluble species. The acid dyes themselves arefrequently more soluble in the solvents employed in this invention than theyare in water. Thus the dyeing rate of the acid dyes and their penetration into the pores of the anodized coating are improved. Since the process of this invention permits the use of more concentrated dye solutions, it is now possible to utilize smaller dye tanks, shorter dyeing periods and more flexible dyeing methods, such as spraying and brushing. The process of this invention makes it possible for the first time to apply water-insoluble colors successfully, rapidly and in 'a variety of strengths. This means an extension of shade rangeand fastness qualities. Thus a greater range of dyes is now available, a distinct advantage in the selection of dyes .for use in dye mixtures. The use otmixtures for colormatchingis now more;feasible'since the various color components remainin 'solu-. tion and can be applied evenly in deep shades.

A significant advance achieved by'the process of the present invention is thatthe colored anodizedaluminum exhibits extremely good light-fastness which, in terms of Fade-Ometer hours, approaches and often exceeds v1000 hours. This superior light fastness means that the colored anodized aluminumniay be employed in exterior construction.

The following examples will better illustrate thenature of the present invention; however, the invention is not intended to be limited to these examples. Parts are by weight unless otherwiseindicated.

EXAMPLE 1 A saturated solution of dye (see table below) is made up in dimethylformarnide. Anodized aluminum (0.8 mil oxide coating) is immersed in this dye solution at room temperature (20 to 25 C.) for 5 minutes. The solvent is then removed by evaporation,'preferably with application of heat. The colored aluminum is then sealed by boiling in water for'30 minutes. Deep, level shades are obtained.

.Table .1

Light iastness Dye structure Color in Fadeiometer hours Na+ Yellow".-. 1,000+

The 1:2 Cr complex of the azo dye; anthrauilie acid 3- I methyl-1-phenyl-5-pyrazoloue.

,(B) The 1:2 Cr complex of the azo dye; 2-arnlno-lephenol-4rsul- Orange.-- 500+ tonamtde 3-methyl-1-phenyl-s-pyrazolone.

(O) The 1:2 Cr complex of equal mole ratios of the'twoazos dyes; Red 500+ 4-chloro-2-aminoanisole 3-methyl-l-phenyl-5-pyrazolone and 4-ehloro-2-aminoanisole ,3-methyl-1-(p-sulfophenyhvo-pyrazolone. Similar results are obtained when the coupling component in the second azodyeistheisomerio 3-methyl-1-(m-sulfophenyl) 5-py'razolone. :(D) The 1:2 Cr complex'of the azodye;'4-ch1oro-2aminoanlsole Violet--." 7500+ 2-naphthol-fi-sulfonamide. s (E) Tge 1211211: tlzomplex of the azo-dye; 2,5-dimethoxyaniline') Blue 750+ map 0 I (F) Tge 1215;} elomplex of the azo dye; 2-a1m'no-4-11itrophenol v Brown 7 1,200+

-nap o.' a v (G) The 1:2 Cr complex of the azo dye; lz-amino-fimitro-Z-naph- .Blaekflsa, 1,500+

'thoM-sulfonlc acid- 2-naphthol.

Table I-Continued Light fastness Dye structure Color in Fadeometer hours HINOQS (EH3 N -N=N /Co\ 2N3: Yellow-.. 500+ O O -N=N l I J SOgNHz The 1:2 Co complex of the azo dye; 2-amlno-1-pheuoM-sulfonamide- 3-methyl-l-phenyl-5-pyrezolone. (I) The 1:2 Co complex of the azo dye; 2-amino-1-phenol 1-sul- Yellow... 1, 000+ fonamideneetoacetanilide. (J) The 1:2 00 complex of the azo dye; Z-amlno-l-phenol--sul- Red 500+ tonamide 2-naphthol.

The following variations in the process of this example may be employed: (a) The anodized aluminum may be immersed in the saturated dye solution at room temperature for a period of time ranging from 5 seconds to 30 minutes depending on the depth of shade desired. Relatively little dye builds up on the aluminum oxide coating beyond that which is achieved after -an immersion of about 5 to minutes. (b) Dimethylf rmamide may be replaced by diethylformamide, dimethylacetamide, diethylacetamide or dimethylsulfoxide. (c) These special solvents may be used in mixtures with other solvents, such as methanol, ethanol, butanol, acetone, methyl ethyl ketone, benzene, toluene, heptane, dioxane, ethylene glycol, carbitol, 2-ethoxy ethanol, pyridine, quinoline, carbontetrachloride, chlorobenzene and linseed oil. This allows the use of lower concentrations where desired for economy, to limit depth of shade or to take advantage of properties of other solvents, such as fast drying and viscosity.

EXAMPLE 2 Polished, thinly anodized sheets of aluminum (0.2 mil oxide coating) are dyed by immersion for 5 minutes at to C. in saturated solutions of the dyes and solvents listed below. The sheets are then rinsed in cold water and sealed by boiling in water for minutes, After drying, the sheets are exposed in a Fade-Ometer for 160, 240 and 320 hours. The results are shown below:

Dye Solvent Depth of shade Light fastness Water. Faint grey. Very poor at 160 hr. Methyl ethyl Weak purp1e Poor at 160 hr.

ketone. V 1 ht b k ery s 1;; rea F of Ex. 1-- Dimethylfofma' m 160 hTS., slightmlde ly more change Dlmethylacetamide- -d0 at 320 hrs.

Dimethylsulfoxide.- -do N 11; change in 320 rs. 2-ethoxyethanol- Weak orange- Destroyed at 160 water. hrs. C of Ex Dgflgghylfmlllfl- }0 W k t 160 h Dimethylacetamiderange 1 er a nt colorrctalned Dlmethylsulfoxldeu after 240 hrs Water Weak violet..- Distroyed at 160 rs. G of Ex. 1-- Methanol .do Do.

Dtmethylforma Violet-black... Some change in 160 mlde. hrs., no further change in 240 hrs.

The above dyeing were intentionally made in pastel shades by employing thinly anodized aluminum in order to accentuate differences in build-up and fastness. With longer dyeing time and heating it is possible to build up heavier shades with better fastness to light. The same relative build-up and light fastness positions are held, however. Only with the solvents of the subject process can heavy shades with excellent light fastness be achieved.

EXAMPLE 3 A saturated solution of the dye (G) of Example 1 is prepared in dimethylformamide. 1 Part of this solution is added to 9 parts of linseed oil and applied in a pattern to anodized aluminum (0.8 mil coating) via a print-' ing device. After heating and sealing, as described in Example 1, a level, light-fast black color is formed.

Similar results are obtained when diethylformamide, dimethylacetamide, diethylacetamide or dimethylsulfoxide is employed as solvent in this example.

EXAMPLE 4 To 1 part of a saturated solution of the dye (G) of Example 1 in dimethylformamide, was added 9 parts of chlorobenzene. An anodized aluminum article (0.8 mil oxide coating) is colored by immersion in this solution for 5 minutes, followed by heating and sealing as described in Example 1. A level, light-fast black dyeing is obtained.

EXAMPLE 5 A saturated solution of the dye (G) of Example 1 in dimethylfonnamide is diluted with methyl ethyl ketone until the final solution contains 10 percent by weight of dimethylformamide. This solution is sprayed onto anodized aluminum (0.8 mil oxide coating) and subsequently heated and sealed as in Example 1 to give a light-fast black color in deep, level shade.

Similar results are obtained when acetone is employed instead of methyl ethyl ketone.

EXAMPLE 6 One part of the dye of Example 1 (G) is dissolved in 5 parts of dimethylformamide and the solution is painted onto anodized aluminum (0.6 mil oxide coating). After evaporation of solvent and sealing the dyed oxide coating in boiling water as described in Example 1, a deep, level light-fast black coloration is obtained.

As many widely different embodiments of this invenmomma scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

What is claimed is:

1. In the process of coloring anodized aluminumwith a dye followed by sealing of the dye in the aluminum oxide coating, the improvement which comprises employing a dye solution containing from 5 to 100 percent by weight of the liquid portion thereof of a solvent for the dye, said solvent being a compound selected from the group consisting of dimethylformamide, diethy1formamide, dimethylacetamide, diethylacetamide and dimethyl-' sulfoxide.

2. A process for coloring anodized aluminum which comprises coating said aluminum with a solution of a. metal complex of an azo dye, said metal being selected from the group consisting of chromium and cobalt and said azo dye being selected from the group consisting of o,o-dihydroxy azo dyes and o-hydroxy-o-carboxy azo dyes, said solution containing from 5 to 100 percent by weight of the liquid portion thereof of a solvent selected from the group consisting of dimethylformamide, dieethylformamide, dimethylacetamide, diethylacetamide and dimethylsulfoxide, heating the coated anodized aluminum to remove the solvent for said .azo dye and finally sealing the color, in the anodized aluminum by treating with hot water.

3. A process according to claim 2 wherein the solvent is dimethylformamide.

4. A process according to claim 3 wherein the dye is the 1:2 chromium complex of the-azo dye obtained by coupling the diazo of l-amino-6-nitro-2-naphthol-4-sultonic acid with Z-naphthol. I

5. .-A process according to claim 3 wherein the dye is the 1:2 chromium complex of theazo dye obtained by coupling the diazo of 2-amino-4-nitrophenol. with 2- naphthol.

References Cited in the fileof this patent UNITED STATES PATENTS OTHER REFERENCES Dimethyl Formamide Product Information, 9 pages, published by Grasseli Chemical Dept. of Du Pont de Nemours & Co. in 1950.

Notice of Adverse Eeeision in Interference In Interference No. 93,7 55 involving Patent No. 3,019,13, R. Dessauer, Process of coloring anodized aluminum, final judgment adverse to the patentee was rendered July 22, 1964, as to claim 1.

[Ofiicz'al Gazette N ovembev" 24, 1964.] 

1. IN THE PROCESS OF COLORING ANODIZED ALUMINUM WITH A DYE FOLLOWED BY SEALING OF THE DYE IN THE ALUMINUM OXIDE COATING, THE IMPROVEMENT WHICH COMPRISES EMPLOYING A DYE SOLUTION CONTAINING FROM 5 TO 100 PERCENT BY WEIGHT OF THE LIQUID PORTION THEREOF OF A SOLVENT FOR THE DYE, SAID SOLVENT BEING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF DIMETHYLFORMAMIDE, DIETHYLFORMAMIDE, DIMETHYLACACETAMIDE, DIETHYLACETAMIDE AND DIMETHYLSULFOXIDE. 